A. Field of the Invention
This invention relates generally to an improvement in illuminated devices such as electronic timepieces equipped for a conventional analog or digital display, indicator gauges, which may comprises a meter panel, directional gauges, ornamentation displays of an image, logo or design, and other similar articles which are illuminated for viewing under poor lighting conditions.
B. Description of the Prior Art
Historically, watches, gauges and other similar articles were first illuminated by using phosphorescent markings. However, when both the manufacturing methods of phosphorescent materials and the materials themselves proved to be medically and environmentally unacceptable, other illuminating means were developed. Some of these other means include the use of LED, LCD, and fluorescent devices, as well as incandescent bulbs. All of these proved to be unsatisfactory, especially for small devices such as wrist watches.
Additionally, these devices could not provide sufficient illumination due to a non-uniformity in brightness across the illuminated display surface. The insufficient illumination was the result of the positioning or shape of the light source itself which was either a point or linear source thereby making these illumination devices limited and unacceptable.
Recently, electroluminescent lighting, hereinafter referred to as EL, was introduced, for an analog or digital watches as another known alternative. An EL element is positioned underneath the watch dials, or other surfaces, or alternatively the dials themselves are made of an EL material, as described in U.S. Pat. Nos. 3,749,977-Sliker, 4,775,964-Alessio & Olsen, 4,208,869-Hanaoka, 5,029,046-Kamede 5,117,334-Kamede. In all of these references direct illumination is provided upward towards the viewer, restricting any aesthetic aspects such as a full color logo or colored images on the dial. Another disadvantage of EL's is that they require complicated auxiliary circuitry. Moreover, the lighting colors are determined by phosphorus contents of the EL, and are limited commercially to colors such as blue-green, white and yellow.